洛谷P1120 小木棍 [数据加强版]搜索

玄学剪支,正好复习一下搜索
感觉搜索题的套路就是先把整体框架打出来,然后再一步一步优化剪枝
1.从maxv到sumv/2枚举长度(想一想,为什么)
2. 开一个桶,从大到小开始枚举
3. 在搜索中,枚举到长度为x的木棍,则下一步也从x开始枚举
4. 如果当前长度为0或target却无解则break掉,很玄学QAQ….

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn = 4000;
int w[maxn];
int  sumv, minv, maxv;
void dfs(int nums,int cur,int target,int p)
{
    if(nums == 0)
    {
        printf("%d",target);
        exit( 0 );
    }
    if(cur == target)
    {
        dfs(nums-1,0,target,maxv);
        return;
    }
    for(int i = p;i >= minv;--i)
        if(w[i] && i + cur <= target)
        {
            w[i] -= 1;
            dfs(nums,cur + i, target, i);                    
            w[i] += 1;
            if (cur == 0 || cur + i == target )  break;
        } 
    return;
}
int main()
{
   // freopen("input.txt","r",stdin);
    int n;
    scanf("%d",&n);
    minv = maxn, maxv = -1;
    for(int i=1;i <= n; ++i)
    {
        int tmp;
        scanf("%d",&tmp);
        if(tmp > 50) continue;
        w[tmp] += 1;
        sumv += tmp;
        minv = min(minv,tmp);
        maxv = max(maxv,tmp);
    }
    for(int i = maxv;i <= sumv/2; ++i)
    {
        if(sumv % i != 0)continue;
        dfs(sumv/i,0,i,maxv);
    }
    printf("%d",sumv);
    return 0;
}
posted @ 2018-08-25 14:37  EM-LGH  阅读(114)  评论(0编辑  收藏  举报